The present invention relates to a line shaft conveyor which is particularly suited to high speed applications.
In the past, most high speed conveyors were made using flat belts or chains to drive the conveyor rollers. These conveyors generally cannot run at rates about 240 feet per minute, due to the limitation in chain speed, bearing limitations, or chain or belt vibrations. These chain and belt drives also had to be broken into sections with separate drives for long conveyors, due to the limited capacity of the chains or belts used to drive the conveyor.
Twisted belt line shaft conveyors are also known in the art. These conveyors do not have to be broken into sections for a long drive as do the belt-driven or chain-driven conveyors, but they cannot be driven at high speeds, because the twisted belts which wrap around the drive shaft and the conveyor rolls have very little surface area contact for driving, and they will slip and fail at high speeds.
Conveyors are known which use a bevel gear or worm gear drive between the line shaft and the conveyor rollers, but these are expensive to manufacture, difficult to maintain, due to the requirements of lubrication, and not suitable for high speed applications for several reasons. For example, the gear sets require precise location for proper drive on the pitch line to reduce noise and wear. High speed gear sets need an enclosed housing to provide lubrication, which adds expense to the conveyor. Also, it is not possible to compensate for the wear of the gears, so gears would have to be replaced frequently in a high speed application. Thus, it would be very impractical to drive a high speed conveyor by means of gears.
Some line shaft conveyors are known to use friction wheels to transmit drive from the drive shaft to the conveyor roller, but these conveyors have not been commercially successful. The friction wheel drives typically have at least one wheel which has very little contact surface for driving (i.e., point contact), so the wheels wear out quickly and slip at high speeds. These designs attempt to mimic the twisted belt line shaft conveyors, which, as mentioned above, are not at all suited to high speed applications.